In recent days, U.S. officials have said that they have evidence that Syrian government forces are preparing chemical weapons ahead of a planned assault on Idlib.

On Monday, U.S. President Donald Trump's national security adviser said the United States, Britain and France had agreed that another use of chemical weapons by the Syrian government would result in a "much stronger response" compared to previous air strikes.

Erdogan said that a focus on the potential use of chemical weapons alone was not enough.

"It is crucial for the U.S., which has concentrated on chemical attacks, to reject its arbitrary hierarchy of death. Conventional weapons are responsible for far more deaths," he said.

Both Turkey and the United Nations have previously warned of a massacre and humanitarian catastrophe involving tens of thousands of civilians in the event of a full-scale offensive.